The present invention relates to passenger airbag apparatuses for automobiles, and more particularly to a passenger airbag apparatus including a deployment-limiting sheet that limits the form of an airbag during inflation.
An exemplary passenger airbag apparatus includes a retainer arranged inside a dashboard, a folded airbag arranged in the retainer, an inflator configured to inflate the airbag, and a lid configured to lid the retainer.
Japanese Patent No. 3406277 (Patent Document 1) discloses in paragraph 0002 that, when an airbag is deployed into a cabin by gas generated from an inflator in the event of a collision of a vehicle, an airbag having a small volume in an initial deployment phase is rapidly inflated, whereas an airbag having a large volume in an initial deployment phase is gradually inflated. The airbag tears a fragile portion of a lid during the inflation and is deployed into the cabin. Hence, a protruding speed of the airbag into the cabin immediately after the lid is torn can become high.
In the Patent Document 1, a strip-shaped deployment-limiting sheet having a predetermined length is provided between the folded airbag and an inner surface of the lid. One end of the deployment-limiting sheet is fixed to a rear edge of a retainer, and the other end thereof extends along the folded airbag from a rear portion to a front portion of the airbag.
When the airbag is inflated, the deployment-limiting sheet extends along the rear portion of the airbag during the inflation, wherein one end of the deployment-limiting sheet is coupled to the rear edge of the retainer and the other end thereof is a free end. Friction is generated between the deployment-limiting sheet and the rear portion of the airbag. Due to the friction, a front portion of the airbag is deployed first, and the rear portion of the airbag is deployed next.
Japanese Unexamined Patent Application Publication No. 2000-247199 (Patent Document 2) discloses a loop-like deployment-limiting sheet, which extends from a rear side through an upper side to a front side of an airbag, and both ends in a front-rear direction of the deployment-limiting sheet are coupled to a retainer. In the deployment-limiting sheet disclosed in the Patent Document 2, a sewing portion is formed by sewing intermediate portions near one end and the other end with respect to the center in the longitudinal direction of the deployment-limiting sheet. Also, a tear line extending across the deployment-limiting sheet is formed at a portion near the center with respect to the sewing portions in the longitudinal direction of the deployment-limiting sheet.
In the Patent Document 2, the sewing portion temporarily limits deployment of the airbag in an initial deployment phase of the airbag. When the sewing portion is torn by an inflation pressure of the airbag, the airbag is inflated until the deployment-limiting sheet achieves a maximum deployment form. At this time, a deployment force of the airbag is consumed by tearing the sewing portion. Accordingly, a deployment speed of the airbag to an occupant is decreased.
When the inflation of the airbag is in a condition where the deployment-limiting sheet achieves the maximum deployment form, the deployment-limiting sheet temporarily restrains further inflation of the airbag. Thereafter, the deployment-limiting sheet is torn at the tear line by the inflation pressure of the airbag, the inflation of the airbag further progresses from the torn part of the tear line, and the airbag achieves a maximum inflation form.
In the Patent Documents 1 and 2, when the airbag is not inflated, the deployment-limiting sheet is interposed between the folded airbag and the lid while the deployment-limiting sheet is folded.
However, according to the Patent Documents 1 and 2, since the deployment-limiting sheet is merely folded and arranged between the folded airbag and the lid, the deployment-limiting sheet may likely be unfolded or deviated from its expected position.
An object of the present invention is, in a passenger airbag apparatus including a deployment-limiting sheet, to provide an airbag apparatus capable of retaining a folded deployment-limiting sheet in a predetermined condition before the inflation.
Further objects and advantages of the invention will be apparent from the following description of the invention.